A CHOLINERGIC CONTRIBUTION TO THE CIRCULATORY RESPONSES EVOKED AT THE ONSET OF HANDGRIP EXERCISE IN HUMANS
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Colleges, School and Institutes
A cholinergic (muscarinic) contribution to the initial circulatory response to exercise in humans remains controversial. Herein we posit that this may be due to exercise mode with a cholinergic contribution being important during isometric handgrip exercise where the hyperaemic response of the muscle is relatively small compared to the onset of leg cycling where a marked increase in muscle blood flow rapidly occurs as a consequence of multiple redundant mechanisms. We recorded blood pressure (BP, brachial artery), stroke volume (pulse contour analysis), cardiac output and systemic vascular resistance (SVR) in young healthy males while performing either 20 s of isometric handgrip contraction at 40% maximum voluntary contraction (Protocol 1; n=9) or 20 s of low intensity leg cycling exercise (Protocol 2; n=8, 42±8 Watts). Exercise trials were conducted under control (no drug) conditions and following cholinergic blockade (glycopyrrolate). Under control conditions isometric handgrip elicited an initial increase in BP (+5±2 mmHg at 3 s and +3±1 mmHg at 10 s, P<0.05), while SVR dropped after 3 s (-27±6% at 20 s; P<0.05). Cholinergic blockade abolished the isometric handgrip-induced fall in SVR and thereby augmented the pressor response (+13±3 mmHg at 10 s; P<0.05 vs. control). In contrast, cholinergic blockade had a non-significant effect on changes in BP and SVR at the onset of leg cycling exercise. These findings suggest that a cholinergic mechanism is important for the BP and SVR responses at the onset of isometric handgrip exercise in humans.
|Journal||AJP Regulatory Integrative and Comparative Physiology|
|Publication status||Published - 14 Jan 2015|